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Midway Middle School

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Chemical Reactions often cause observable changes

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Color Odor Release or Absorption of Heat Release or Absorption of Light Release of Gas

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Examples of Physical Changes *Melting ice *Dissolving salt *Cutting paper

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*No new product is formed *Substance just physically appears different

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Examples of Chemical Changes *Color change *Heat absorbed or released *Formation of gas

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*Elements are made of only one kind of atom *Elements are all listed on the periodic table Examples of elements: Oxygen O Iron Fe Sodium - Na

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*Compounds are made of two or more elements chemically combined Examples of compounds: Water H 2 O Baking soda NaHCO 3 Carbon dioxide CO 2

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NaHCO 3 This is the chemical formula for baking soda. *How many elements are there? 4 Sodium(Na) Hydrogen(H) Carbon(C) Oxygen(O )

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NaHCO 3 This is the chemical formula for baking soda. *How many total atoms are there? 6 1 - Sodium(Na) 1 - Hydrogen(H) 1 - Carbon(C) 3 - Oxygen(O )

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Matter can NOT be created Nor can it be destroyed Chemical Equations MUST balance

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The same number of atoms of each element must be in the products that were in the reactants of a chemical equation. Example: ReactantsProduct

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Chemical reactions are represented on paper by chemical equations. Example: 2 hydrogen gas (2H 2 ) can react (burn) with oxygen gas (O 2 ) to form 2 water molecules(H 2 0).

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yields subscript

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Why do Chemical Equations have to balance?

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Is this a balanced equation? Yes atoms in = atoms out

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Balance the following equation:

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We seem to be o.k. with our number of (C)carbon atoms in both the reactants and products But, we have only half the (H)hydrogen in our products as in our reactants.

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2

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*This has balanced our (C)carbon and (H)hydrogen atoms *But, we now have 4 (O)oxygen atoms in our products, and only have 2 in our reactants.

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2

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We have a balanced chemical equation for the reaction of methane with oxygen.